The Surgeon General's report on "Smoking and Health" in 1964 first identified the connection between smoking and respiratory disease. Yet cigarette smoking will cause 393,000 premature deaths in the United States alone this year. Secondhand smoke – airborne tobacco smoke inhaled by those other than the smoker – will prematurely kill another 49,000 Americans this year.

And now, attention is focusing on "thirdhand smoke" – the chemical and particle byproducts of tobacco smoke that land on surfaces in an environment but are later relaunched into the air after combining with other airborne contaminants.

Tobacco-smoke dangers lurk for months

More than two months after a smoker has moved out of an apartment or other indoor environment, residual nicotine on surfaces reacts with airborne ozone and nitrous acid to form a frightening new round of airborne pollutants, including cancer-causing ultrafine particles. The noxious air pollutants are capable of causing DNA damage that leads to genetic mutations associated with many types of cancer. Some scientists think thirdhand smoke may turn out to be the most lethal form of smoke of all.

Now a new study, "Thirdhand smoke causes DNA damage in human cells," from the Lawrence Berkeley National Laboratory confirms the link between thirdhand smoke and genetic damage in human cells. The study was published in late June in the scientific journal Mutagenesis. Lawrence Berkeley Lab is managed by the University of California on behalf of the U.S. Department of Energy. The lab has been awarded 13 Nobel prizes since its founding in 1931.

Hotel rooms and nicotine residues

For non-smokers this may be a concern when staying at hotels. Anyone who has ever walked into a "non-smoking" hotel room and noticed a tobacco smoke odor will not be surprised that research shows when hotels allow smoking in any of its rooms, the smoke gets intoallof its rooms.

A study published in the journal Tobacco Control found that nicotine residues and other chemical traces in smoking rooms end up in hallways and in other rooms, including non-smoking rooms. They found smoke residue on surfaces and in the air of both smoking and non-smoking rooms in 30 California hotels where smoking was allowed. Levels were highest in the smoking rooms, but levels in non-smoking rooms were much higher than those found at 10 smoke-free hotels.

Chemical transformation of nicotine

The Berkeley Lab study reports that when nicotine in thirdhand smoke is united with nitrous acids in the air, the nicotine "undergoes a chemical transformation" and forms into a number of cancer-causing chemical compounds known as "nitrosamines." The nicotine also reacts with ozone in the air to form ultrafine particles which carry harmful chemicals into human tissue through inhalation, ingestion or even skin contact.

Common cleaning methods do little do clear the toxic substances such as nicotine from the environment, according to the researchers. And the thirdhand smoke substances become more toxic, not less, over time. Test strips exposed to the smoke of five cigarettes in 20 minutes were found to contain lower concentrations of gene-damaging compounds than "chronic samples" – test strips exposed to less smoke over 196 days. The researchers then exposed human cells to the test substances to determine gene-mutating effects.

Best solution: Never allow smoking indoors

The best solution to counter the effects of first-, second- or third-hand smoke is to never allow smoking in an indoor environment in the first place. Tobacco smoke contains more than 4,000 different chemicals, 60 of which are known carcinogens. These various elements are a mix of liquids, gases, and solid particles.

While the use of an air purifier cannot reduce firsthand exposure to tobacco smoke, it may reduce exposure to secondhand smoke and deposition of residues involved in thirdhand smoke. In any case, air purification remains a distant second to never allowing smoking in an indoor environment to begin with. And only an air purifier that provides a high level of efficiency against both particles and gases – for example, the IQAir GC MultiGas – can be effective in helping to fight tobacco smoke.